Physicochemical Properties of the Mammalian Molecular Chaperone HSP60

Molecular Chaperonin HSP60: Current Understanding and Future Prospects

Molecular chaperones are highly conserved across evolution and play a crucial role in preserving protein homeostasis. The 60 kDa heat shock protein (HSP60), also referred to as chaperonin 60 (Cpn60), resides within mitochondria and is involved in maintaining the organelle's proteome integrity and homeostasis. The HSP60 family, encompassing Cpn60, plays diverse roles in cellular processes, including protein folding, cell signaling, and managing high-temperature stress. In prokaryotes, HSP60 is well understood as a GroEL/GroES complex, which forms a double-ring cavity and aids in protein folding. In eukaryotes, HSP60 is implicated in numerous biological functions, like facilitating the folding of native proteins and influencing disease and development processes. Notably, research highlights its critical involvement in sustaining oxidative stress and preserving mitochondrial integrity. HSP60 perturbation results in the loss of the mitochondria integrity and activates apoptosis. Currently, numerous clinical investigations are in progress to explore targeting HSP60 both in vivo and in vitro across various disease models. These studies aim to enhance our comprehension of disease mechanisms and potentially harness HSP60 as a therapeutic target for various conditions, including cancer, inflammatory disorders, and neurodegenerative diseases. This review delves into the diverse functions of HSP60 in regulating proteo-homeostasis, oxidative stress, ROS, apoptosis, and its implications in diseases like cancer and neurodegeneration.

Heat Shock Proteins, a Double-Edged Sword: Significance in Cancer Progression, Chemotherapy Resistance and Novel Therapeutic Perspectives

Heat shock proteins (Hsps) are involved in one of the adaptive mechanisms protecting cells against environmental and metabolic stress. Moreover, the large role of these proteins in the carcinogenesis process, as well as in chemoresistance, was noticed. This review aims to draw attention to the possibilities of using Hsps in developing new cancer therapy methods, as well as to indicate directions for future research on this topic. In order to discuss this matter, a thorough review of the latest scientific literature was carried out, taking into account the importance of selected proteins from the Hsp family, including Hsp27, Hsp40, Hsp60, Hsp70, Hsp90 and Hsp110. One of the more characteristic features of all Hsps is that they play a multifaceted role in cancer progression, which makes them an obvious target for modern anticancer therapy. Some researchers emphasize the importance of directly inhibiting the action of these proteins. In turn, others point to their possible use in the design of cancer vaccines, which would work by inducing an immune response in various types of cancer. Due to these possibilities, it is believed that the use of Hsps may contribute to the progress of oncoimmunology, and thus help in the development of modern anticancer therapies, which would be characterized by higher effectiveness and lower toxicity to the patients.

Oligomeric State and Holding Activity of Hsp60

Similar to its bacterial homolog GroEL, Hsp60 in oligomeric conformation is known to work as a folding machine, with the assistance of co-chaperonin Hsp10 and ATP. However, recent results have evidenced that Hsp60 can stabilize aggregation-prone molecules in the absence of Hsp10 and ATP by a different, "holding-like" mechanism. Here, we investigated the relationship between the oligomeric conformation of Hsp60 and its ability to inhibit fibrillization of the Ab40 peptide. The monomeric or tetradecameric form of the protein was isolated, and its effect on beta-amyloid aggregation was separately tested. The structural stability of the two forms of Hsp60 was also investigated using differential scanning calorimetry (DSC), light scattering, and circular dichroism. The results showed that the protein in monomeric form is less stable, but more effective against amyloid fibrillization. This greater functionality is attributed to the disordered nature of the domains involved in subunit contacts.

Potential application of heat shock proteins as therapeutic targets in Parkinson's disease

Parkinson's disease (PD) is a common chronic neurodegenerative disease, and the heat shock proteins (HSPs) are proved to be of great value for PD. In addition, HSPs can maintain protein homeostasis, degrade and inhibit protein aggregation by properly folding and activating intracellular proteins in PD. This study mainly summarizes the important roles of HSPs in PD and explores their feasibility as targets. We introduced the structural and functional characteristics of HSPs and the physiological functions of HSPs in PD. HSPs can protect neurons from damage by degrading aggregates with three mechanisms, including the aggregation and removing α-Synuclein (α-Syn) aggregates, promotion the autophagy of abnormal proteins, and inhibition the apoptosis of degenerated neurons. This study underscores the importance of HSPs as targets in PD and helps to expand new mechanisms in PD treatment strategies.

Interlinked role of ASN, TDP-43 and Miro1 with parkinopathy: Focus on targeted approach against neuropathy in parkinsonism

Parkinsonism is a complex neurodegenerative disease that is difficult to differentiate because of its idiopathic and unknown origins. The hereditary parkinsonism known as autosomal recessive-juvenile parkinsonism (AR-JP) is marked by tremors, dyskinesias, dystonic characteristics, and manifestations that improve sleep but do not include dementia. This was caused by deletions and point mutations in PARK2 (chromosome 6q25.2-27). Diminished or unusual sensations (paresthesias), loss of neuron strength both in the CNS and peripheral nerves, and lack of motor coordination are the hallmarks of neuropathy in parkinsonism. The incidence of parkinsonism during oxidative stress and ageing is associated with parkinopathy. Parkinopathy is hypothesized to be triggered by mutation of the parkin (PRKN) gene and loss of normal physiological functions of PRKN proteins, which triggers their pathogenic aggregation due to conformational changes. Two important genes that control mitochondrial health are PRKN and phosphatase and tensin homologue deleted on chromosome 10-induced putative kinase 1 (PINK1). Overexpression of TAR DNA-binding protein-43 (TDP-43) increases the aggregation of insoluble PRKN proteins in OMM. Foreign α-synuclein (ASN) promotes parkinopathy via S-nitrosylation and hence has a neurotoxic effect on dopaminergic nerves. Miro1 (Miro GTPase1), a member of the RAS superfamily, is expressed in nerve cells. Due to PINK1/PRKN and Miro1's functional relationship, an excess of mitochondrial calcium culminates in the destruction of dopaminergic neurons. An interlinked understanding of TDP-43, PINK1/PRKN, ASN, and Miro1 signalling in the communication among astrocytes, microglia, neurons, and immune cells within the brain explored the pathway of neuronal death and shed light on novel strategies for the diagnosis and treatment of parkinsonism.

Local Flexibility of a New Single-Ring Chaperonin Encoded by Bacteriophage AR9 Bacillus subtilis

Chaperonins, a family of molecular chaperones, assist protein folding in all domains of life. They are classified into two groups: bacterial variants and those present in endosymbiotic organelles of eukaryotes belong to group I, while group II includes chaperonins from the cytosol of archaea and eukaryotes. Recently, chaperonins of a prospective new group were discovered in giant bacteriophages; however, structures have been determined for only two of them. Here, using cryo-EM, we resolved a structure of a new chaperonin encoded by gene 228 of phage AR9 B. subtilis. This structure has similarities and differences with members of both groups, as well as with other known phage chaperonins, which further proves their diversity.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Host cell stress response as a predictor of COVID-19 infectivity and disease progression

The coronavirus disease (COVID-19) caused by a coronavirus identified in December 2019 has caused a global pandemic. COVID-19 was declared a pandemic in March 2020 and has led to more than 6.3 million deaths. The pandemic has disrupted world travel, economies, and lifestyles worldwide. Although vaccination has been an effective tool to reduce the severity and spread of the disease there is a need for more concerted approaches to fighting the disease. COVID-19 is characterised as a severe acute respiratory syndrome . The severity of the disease is associated with a battery of comorbidities such as cardiovascular diseases, cancer, chronic lung disease, and renal disease. These underlying diseases are associated with general cellular stress. Thus, COVID-19 exacerbates outcomes of the underlying conditions. Consequently, coronavirus infection and the various underlying conditions converge to present a combined strain on the cellular response. While the host response to the stress is primarily intended to be of benefit, the outcomes are occasionally unpredictable because the cellular stress response is a function of complex factors. This review discusses the role of the host stress response as a convergent point for COVID-19 and several non-communicable diseases. We further discuss the merits of targeting the host stress response to manage the clinical outcomes of COVID-19.

Heat shock protein 60 couples an oxidative stress-responsive p38/MK2 signaling and NF-κB survival machinery in cancer cells

Mitochondria communicate with other cellular compartments via the secretion of protein factors. Here, we report an unexpected messenger role for heat shock protein 60 (HSP60) as a mitochondrial-releasing protein factor that couples stress-sensing signaling and cell survival machineries. We show that mild oxidative stress predominantly activates the p38/MK2 complex, which phosphorylates mitochondrial fission factor 1 (MFF1) at the S155 site. Such phosphorylated MFF1 leads to the oligomerization of voltage anion-selective channel 1, thereby triggering the formation of a mitochondrial membrane pore through which the matrix protein HSP60 passes. The liberated HSP60 associates with and activates the IκB kinase (IKK) complex in the cytosol, which consequently induces the NF-κB-dependent expression of survival genes in nucleus. Indeed, inhibition of the HSP60 release or HSP60-IKK interaction sensitizes the cancer cells to mild oxidative stress and regresses the tumorigenic growth of cancer cells in the mouse xenograft model. Thus, this study reveals a novel mitonuclear survival axis responding to oxidative stress.

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Mitochondria release the matrix protein HSP60 to the cytosol under mild oxidative stress.

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Mild oxidative stress activates p38/MK2 complex, which phosphorylates MFF1 at S155 site.

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MFF1 phosphorylation triggers the VDAC1 oligomerizationto form a mitochondrial membrane pore for the HSP60 release.

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The released HSP60 activates the IKK/NF-κB survival signaling in the in vitro and in vivo models.

Stress-induced inflammation evoked by immunogenic cell death is blunted by the IRE1α kinase inhibitor KIRA6 through HSP60 targeting

Mounting evidence indicates that immunogenic therapies engaging the unfolded protein response (UPR) following endoplasmic reticulum (ER) stress favor proficient cancer cell-immune interactions, by stimulating the release of immunomodulatory/proinflammatory factors by stressed or dying cancer cells. UPR-driven transcription of proinflammatory cytokines/chemokines exert beneficial or detrimental effects on tumor growth and antitumor immunity, but the cell-autonomous machinery governing the cancer cell inflammatory output in response to immunogenic therapies remains poorly defined. Here, we profiled the transcriptome of cancer cells responding to immunogenic or weakly immunogenic treatments. Bioinformatics-driven pathway analysis indicated that immunogenic treatments instigated a NF-κB/AP-1-inflammatory stress response, which dissociated from both cell death and UPR. This stress-induced inflammation was specifically abolished by the IRE1α-kinase inhibitor KIRA6. Supernatants from immunogenic chemotherapy and KIRA6 co-treated cancer cells were deprived of proinflammatory/chemoattractant factors and failed to mobilize neutrophils and induce dendritic cell maturation. Furthermore, KIRA6 significantly reduced the in vivo vaccination potential of dying cancer cells responding to immunogenic chemotherapy. Mechanistically, we found that the anti-inflammatory effect of KIRA6 was still effective in IRE1α-deficient cells, indicating a hitherto unknown off-target effector of this IRE1α-kinase inhibitor. Generation of a KIRA6-clickable photoaffinity probe, mass spectrometry, and co-immunoprecipitation analysis identified cytosolic HSP60 as a KIRA6 off-target in the IKK-driven NF-κB pathway. In sum, our study unravels that HSP60 is a KIRA6-inhibitable upstream regulator of the NF-κB/AP-1-inflammatory stress responses evoked by immunogenic treatments. It also urges caution when interpreting the anti-inflammatory action of IRE1α chemical inhibitors.

Structural basis for the structural dynamics of human mitochondrial chaperonin mHsp60

Human mitochondrial chaperonin mHsp60 is essential for mitochondrial function by assisting folding of mitochondrial proteins. Unlike the double-ring bacterial GroEL, mHsp60 exists as a heptameric ring that is unstable and dissociates to subunits. The structural dynamics has been implicated for a unique mechanism of mHsp60. We purified active heptameric mHsp60, and determined a cryo-EM structure of mHsp60 heptamer at 3.4 Å. Of the three domains, the equatorial domains contribute most to the inter-subunit interactions, which include a four-stranded β sheet. Our structural comparison with GroEL shows that mHsp60 contains several unique sequences that directly decrease the sidechain interactions around the β sheet and indirectly shorten β strands by disengaging the backbones of the flanking residues from hydrogen bonding in the β strand conformation. The decreased inter-subunit interactions result in a small inter-subunit interface in mHsp60 compared to GroEL, providing a structural basis for the dynamics of mHsp60 subunit association. Importantly, the unique sequences are conserved among higher eukaryotic mitochondrial chaperonins, suggesting the importance of structural dynamics for eukaryotic chaperonins. Our structural comparison with the single-ring mHsp60-mHsp10 shows that upon mHsp10 binding the shortened inter-subunit β sheet is restored and the overall inter-subunit interface of mHsp60 increases drastically. Our structural basis for the mHsp10 induced stabilization of mHsp60 subunit interaction is consistent with the literature that mHsp10 stabilizes mHsp60 quaternary structure. Together, our studies provide structural bases for structural dynamics of the mHsp60 heptamer and for the stabilizing effect of mHsp10 on mHsp60 subunit association.

HSP60 in cancer: a promising biomarker for diagnosis and a potentially useful target for treatment

Heat shock proteins (HSPs), most of which are molecular chaperones, are highly conserved proteins produced by cells under physiological stress or pathological conditions. HSP60 (57-69 kDa) can promote or inhibit cell apoptosis through different mechanisms, and its abnormal expression is also related to tumour cell metastasis and drug resistance. In recent years, HSP60 has received increasing attention in the field of cancer research due to its potential as a diagnostic and prognostic biomarker or therapeutic target. However, in different types of cancer, the specific mechanisms of abnormally expressed HSP60 in tumour carcinogenesis and drug resistance are complicated and still require further study. In this article, we comprehensively review the regulative mechanisms of HSP60 on apoptosis, its applications as a cancer diagnostic biomarker and a therapeutic target, evidence of involvement in tumour resistance and the applications of exosomal HSP60 in liquid biopsy. By evaluating the current findings of HSP60 in cancer research, we highlight some core issues that need to be addressed for the use of HSP60 as a diagnostic or prognostic biomarker and therapeutic target in certain types of cancer.

CREG1 improves the capacity of the skeletal muscle response to exercise endurance via modulation of mitophagy

CREG1 (cellular repressor of E1A-stimulated genes 1) is involved in tissue homeostasis and influences macroautophagy/autophagy to protect cardiovascular function. However, the physiological and pathological role of CREG1 in the skeletal muscle is not clear. Here, we established a skeletal muscle-specific creg1 knockout mouse model (creg1;Ckm-Cre) by crossing the Creg1-floxed mice (Creg1^fl/fl) with a transgenic line expressing Cre recombinase under the muscle-specific Ckm (creatine kinase, muscle) promoter. In creg1;Ckm-Cre mice, the exercise time to exhaustion and running distance were significantly reduced compared to Creg1^fl/fl mice at the age of 9 months. In addition, the administration of recombinant (re)CREG1 protein improved the motor function of 9-month-old creg1;Ckm-Cre mice. Moreover, electron microscopy images of 9-month-old creg1;Ckm-Cre mice showed that the mitochondrial quality and quantity were abnormal and associated with increased levels of PINK1 (PTEN induced putative kinase 1) and PRKN/PARKIN (parkin RBR E3 ubiquitin protein ligase) but reduced levels of the mitochondrial proteins PTGS2/COX2, COX4I1/COX4, and TOMM20. These results suggested that CREG1 deficiency accelerated the induction of mitophagy in the skeletal muscle. Mechanistically, gain-and loss-of-function mutations of Creg1 altered mitochondrial morphology and function, impairing mitophagy in C2C12 cells. Furthermore, HSPD1/HSP60 (heat shock protein 1) (401-573 aa) interacted with CREG1 (130-220 aa) to antagonize the degradation of CREG1 and was involved in the regulation of mitophagy. This was the first time to demonstrate that CREG1 localized to the mitochondria and played an important role in mitophagy modulation that determined skeletal muscle wasting during the growth process or disease conditions.Abbreviations: CCCP: carbonyl cyanide m-chlorophenylhydrazone; CKM: creatine kinase, muscle; COX4I1/COX4: cytochrome c oxidase subunit 4I1; CREG1: cellular repressor of E1A-stimulated genes 1; DMEM: dulbecco's modified eagle medium; DNM1L/DRP1: dynamin 1-like; FCCP: carbonyl cyanide p-trifluoro-methoxy phenyl-hydrazone; HSPD1/HSP60: heat shock protein 1 (chaperonin); IP: immunoprecipitation; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MFF: mitochondrial fission factor; MFN2: mitofusin 2; MYH1/MHC-I: myosin, heavy polypeptide 1, skeletal muscle, adult; OCR: oxygen consumption rate; OPA1: OPA1, mitochondrial dynamin like GTPase; PINK1: PTEN induced putative kinase 1; PPARGC1A/PGC-1α: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PRKN/PARKIN: parkin RBR E3 ubiquitin protein ligase; PTGS2/COX2: prostaglandin-endoperoxide synthase 2; RFP: red fluorescent protein; RT-qPCR: real-time quantitative PCR; SQSTM1/p62: sequestosome 1; TFAM: transcription factor A, mitochondrial; TOMM20: translocase of outer mitochondrial membrane 20; VDAC: voltage-dependent anion channel.

Cardio-Vascular Heat Shock Protein (cvHsp, HspB7), an Unusual Representative of Small Heat Shock Protein Family

HspB7 is one of ten human small heat shock proteins. This protein is expressed only in insulin-dependent tissues (heart, skeletal muscle, and fat tissue), and expression of HspB7 is regulated by many different factors. Single nucleotide polymorphism is characteristic for the HspB7 gene and this polymorphism correlates with cardio-vascular diseases and obesity. HspB7 has an unusual N-terminal sequence, a conservative α-crystallin domain, and very short C-terminal domain lacking conservative IPV tripeptide involved in a small heat shock proteins oligomer formation. Nevertheless, in the isolated state HspB7 forms both small oligomers (probably dimers) and very large oligomers (aggregates). HspB7 is ineffective in suppression of amorphous aggregation of model proteins induced by heating or reduction of disulfide bonds, however it is very effective in prevention of aggregation of huntingtin fragments enriched with Gln residues. HspB7 can be an effective sensor of electrophilic agents. This protein interacts with the contractile and cytoskeleton proteins (filamin C, titin, and actin) and participates in protection of the contractile apparatus and cytoskeleton from different adverse conditions. HspB7 possesses tumor suppressive activity. Further investigations are required to understand molecular mechanisms of HspB7 participation in numerous biological processes.

Mycobacterium tuberculosis RipA Dampens TLR4-Mediated Host Protective Response Using a Multi-Pronged Approach Involving Autophagy, Apoptosis, Metabolic Repurposing, and Immune Modulation

Reductive evolution has endowed Mycobacterium tuberculosis (M. tb) with moonlighting in protein functions. We demonstrate that RipA (Rv1477), a peptidoglycan hydrolase, activates the NFκB signaling pathway and elicits the production of pro-inflammatory cytokines, TNF-α, IL-6, and IL-12, through the activation of an innate immune-receptor, toll-like receptor (TLR)4. RipA also induces an enhanced expression of macrophage activation markers MHC-II, CD80, and CD86, suggestive of M1 polarization. RipA harbors LC3 (Microtubule-associated protein 1A/1B-light chain 3) motifs known to be involved in autophagy regulation and indeed alters the levels of autophagy markers LC3BII and P62/SQSTM1 (Sequestosome-1), along with an increase in the ratio of P62/Beclin1, a hallmark of autophagy inhibition. The use of pharmacological agents, rapamycin and bafilomycin A1, reveals that RipA activates PI3K-AKT-mTORC1 signaling cascade that ultimately culminates in the inhibition of autophagy initiating kinase ULK1 (Unc-51 like autophagy activating kinase). This inhibition of autophagy translates into efficient intracellular survival, within macrophages, of recombinant Mycobacterium smegmatis expressing M. tb RipA. RipA, which also localizes into mitochondria, inhibits the production of oxidative phosphorylation enzymes to promote a Warburg-like phenotype in macrophages that favors bacterial replication. Furthermore, RipA also inhibited caspase-dependent programed cell death in macrophages, thus hindering an efficient innate antibacterial response. Collectively, our results highlight the role of an endopeptidase to create a permissive replication niche in host cells by inducing the repression of autophagy and apoptosis, along with metabolic reprogramming, and pointing to the role of RipA in disease pathogenesis.

Heat shock protein 60 and cardiovascular diseases: An intricate love-hate story

Cardiovascular diseases (CVDs) are the result of complex pathophysiological processes in the tissues comprising the heart and blood vessels. Inflammation is the main culprit for the development of cardiovascular dysfunction, and it may be traced to cellular stress events including apoptosis, oxidative and shear stress, and cellular and humoral immune responses, all of which impair the system's structure and function. An intracellular chaperone, heat shock protein 60 (HSP60) is an intriguing example of a protein that may both be an ally and a foe for cardiovascular homeostasis; on one hand providing protection against cellular injury, and on the other triggering damaging responses through innate and adaptive immunity. In this review we will discuss the functions of HSP60 and its effects on cells and the immune system regulation, only to later address its implications in the development and progression of CVD. Lastly, we summarize the outcome of various studies targeting HSP60 as a potential therapeutic strategy for cardiovascular and other diseases.

Stress proteins: the biological functions in virus infection, present and challenges for target-based antiviral drug development

Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histone-like nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson’s diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

Hsp60 Post-translational Modifications: Functional and Pathological Consequences

Hsp60 is a chaperone belonging to the Chaperonins of Group I and typically functions inside mitochondria in which, together with the co-chaperonin Hsp10, maintains protein homeostasis. In addition to this canonical role, Hsp60 plays many others beyond the mitochondria, for instance in the cytosol, plasma-cell membrane, extracellular space, and body fluids. These non-canonical functions include participation in inflammation, autoimmunity, carcinogenesis, cell replication, and other cellular events in health and disease. Thus, Hsp60 is a multifaceted molecule with a wide range of cellular and tissue locations and functions, which is noteworthy because there is only one hsp60 gene. The question is by what mechanism this protein can become multifaceted. Likely, one factor contributing to this diversity is post-translational modification (PTM). The amino acid sequence of Hsp60 contains many potential phosphorylation sites, and other PTMs are possible such as O-GlcNAcylation, nitration, acetylation, S-nitrosylation, citrullination, oxidation, and ubiquitination. The effect of some of these PTMs on Hsp60 functions have been examined, for instance phosphorylation has been implicated in sperm capacitation, docking of H2B and microtubule-associated proteins, mitochondrial dysfunction, tumor invasiveness, and delay or facilitation of apoptosis. Nitration was found to affect the stability of the mitochondrial permeability transition pore, to inhibit folding ability, and to perturb insulin secretion. Hyperacetylation was associated with mitochondrial failure; S-nitrosylation has an impact on mitochondrial stability and endothelial integrity; citrullination can be pro-apoptotic; oxidation has a role in the response to cellular injury and in cell migration; and ubiquitination regulates interaction with the ubiquitin-proteasome system. Future research ought to determine which PTM causes which variations in the Hsp60 molecular properties and functions, and which of them are pathogenic, causing chaperonopathies. This is an important topic considering the number of acquired Hsp60 chaperonopathies already cataloged, many of which are serious diseases without efficacious treatment.

Human Molecular Chaperone Hsp60 and Its Apical Domain Suppress Amyloid Fibril Formation of α-Synuclein

Heat shock proteins play roles in assisting other proteins to fold correctly and in preventing the aggregation and accumulation of proteins in misfolded conformations. However, the process of aging significantly degrades this ability to maintain protein homeostasis. Consequently, proteins with incorrect conformations are prone to aggregate and accumulate in cells, and this aberrant aggregation of misfolded proteins may trigger various neurodegenerative diseases, such as Parkinson's disease. Here, we investigated the possibilities of suppressing α-synuclein aggregation by using a mutant form of human chaperonin Hsp60, and a derivative of the isolated apical domain of Hsp60 (Hsp60 AD(Cys)). In vitro measurements were used to detect the effects of chaperonin on amyloid fibril formation, and interactions between Hsp60 proteins and α-synuclein were probed by quartz crystal microbalance analysis. The ability of Hsp60 AD(Cys) to suppress α-synuclein intracellular aggregation and cytotoxicity was also demonstrated. We show that Hsp60 mutant and Hsp60 AD(Cys) both effectively suppress α-synuclein amyloid fibril formation, and also demonstrate for the first time the ability of Hsp60 AD(Cys) to function as a mini-chaperone inside cells. These results highlight the possibility of using Hsp60 AD as a method of prevention and treatment of neurodegenerative diseases.

Knockdown of CaHSP60-6 confers enhanced sensitivity to heat stress in pepper (Capsicum annuum L.)

HSP60 gene family in pepper was analyzed through bioinformatics along with transcriptional regulation against multiple abiotic and hormonal stresses. Furthermore, the knockdown of CaHSP60-6 increased sensitivity to heat stress. The 60 kDa heat shock protein (HSP60) also known as chaperonin (cpn60) is encoded by multi-gene family that plays an important role in plant growth, development and in stress response as a molecular chaperone. However, little is known about the HSP60 gene family in pepper (Capsicum annuum L.). In this study, 16 putative pepper HSP60 genes were identified through bioinformatic tools. The phylogenetic tree revealed that eight of the pepper HSP60 genes (50%) clustered into group I, three (19%) into group II, and five (31%) into group III. Twelve (75%) CaHSP60 genes have more than 10 introns, while only a single gene contained no introns. Chromosomal mapping revealed that the tandem and segmental duplication events occurred in the process of evolution. Gene ontology enrichment analysis predicted that CaHSP60 genes were responsible for protein folding and refolding in an ATP-dependent manner in response to various stresses in the biological processes category. Multiple stress-related cis-regulatory elements were found in the promoter region of these CaHSP60 genes, which indicated that these genes were regulated in response to multiple stresses. Tissue-specific expression was studied under normal conditions and induced under 2 h of heat stress measured by RNA-Seq data and qRT-PCR in different tissues (roots, stems, leaves, and flowers). The data implied that HSP60 genes play a crucial role in pepper growth, development, and stress responses. Fifteen (93%) CaHSP60 genes were induced in both, thermo-sensitive B6 and thermo-tolerant R9 lines under heat treatment. The relative expression of nine representative CaHSP60 genes in response to other abiotic stresses (cold, NaCl, and mannitol) and hormonal applications [ABA, methyl jasmonate (MeJA), and salicylic acid (SA)] was also evaluated. Knockdown of CaHSP60-6 increased the sensitivity to heat shock treatment as documented by a higher relative electrolyte leakage, lipid peroxidation, and reactive oxygen species accumulation in silenced pepper plants along with a substantial lower chlorophyll content and antioxidant enzyme activity. These results suggested that HSP60 might act as a positive regulator in pepper defense against heat and other abiotic stresses. Our results provide a basis for further functional analysis of HSP60 genes in pepper.

MitCHAP-60 and Hereditary Spastic Paraplegia SPG-13 Arise from an Inactive hsp60 Chaperonin that Fails to Fold the ATP Synthase β-Subunit

The human mitochondrial heat shock protein 60 (hsp60) is a tetradecameric chaperonin that folds proteins in the mitochondrial matrix. An hsp60 D3G mutation leads to MitCHAP-60, an early onset neurodegenerative disease while hsp60 V72I has been linked to SPG13, a form of hereditary spastic paraplegia. Previous studies have suggested that these mutations impair the protein folding activity of hsp60 complexes but the detailed mechanism by which these mutations lead the neuromuscular diseases remains unknown. It is known, is that the β-subunit of the human mitochondrial ATP synthase co-immunoprecipitates with hsp60 indicating that the β-subunit is likely a substrate for the chaperonin. Therefore, we hypothesized that hsp60 mutations cause misfolding of proteins that are critical for aerobic respiration. Negative-stain electron microscopy and DLS results suggest that the D3G and V72I complexes fall apart when treated with ATP or ADP and are therefore unable to fold denatured substrates such as α-lactalbumin, malate dehydrogenase (MDH), and the β-subunit of ATP synthase in in-vitro protein-folding assays. These data suggests that hsp60 plays a crucial role in folding important players in aerobic respiration such as the β-subunit of the ATP synthase. The hsp60 mutations D3G and V72I impair its ability to fold mitochondrial substrates leading to abnormal ATP synthesis and the development of the MitCHAP-60 and SPG13 neuromuscular degenerative disorders.

An update on the discovery and development of selective heat shock protein inhibitors as anti-cancer therapy

INTRODUCTION

Over the years, not a single HSP inhibitor has progressed into the post-market phase of drug development despite the success recorded in various pre-clinical and clinical studies. The inability of existing drugs to specifically target oncogenic HSPs has majorly accounted for these setbacks. Recent combinatorial strategies that incorporated computer-aided drug design (CADD) techniques are geared towards the development of highly specific HSP inhibitors with increased activities and minimal toxicities. Areas covered: In this review, strategic therapeutic approaches that have recently aided the development of selective HSP inhibitors were highlighted. Also, the significant contributions of CADD techniques over the years were discussed in detail. This article further describes promising computational paradigms and their applications towards the discovery of highly specific inhibitors of oncogenic HSPs. Expert opinion: The recent shift towards highly selective and specific HSP inhibition has shown great promise as evidenced by the development of paralog/isoform-selective HSP drugs. It could be further augmented with computer-aided drug design strategies, which incorporate reliable methods that would greatly enhance the design and optimization of novel inhibitors with improved activities and minimal toxicities.

Heat Shock Proteins in Alzheimer's Disease: Role and Targeting

Among diseases whose cure is still far from being discovered, Alzheimer’s disease (AD) has been recognized as a crucial medical and social problem. A major issue in AD research is represented by the complexity of involved biochemical pathways, including the nature of protein misfolding, which results in the production of toxic species. Considering the involvement of (mis)folding processes in AD aetiology, targeting molecular chaperones represents a promising therapeutic perspective. This review analyses the connection between AD and molecular chaperones, with particular attention toward the most important heat shock proteins (HSPs) as representative components of the human chaperome: Hsp60, Hsp70 and Hsp90. The role of these proteins in AD is highlighted from a biological point of view. Pharmacological targeting of such HSPs with inhibitors or regulators is also discussed.

Using Single-Molecule Approaches to Understand the Molecular Mechanisms of Heat-Shock Protein Chaperone Function

The heat-shock proteins (Hsp) are a family of molecular chaperones, which collectively form a network that is critical for the maintenance of protein homeostasis. Traditional ensemble-based measurements have provided a wealth of knowledge on the function of individual Hsps and the Hsp network; however, such techniques are limited in their ability to resolve the heterogeneous, dynamic and transient interactions that molecular chaperones make with their client proteins. Single-molecule techniques have emerged as a powerful tool to study dynamic biological systems, as they enable rare and transient populations to be identified that would usually be masked in ensemble measurements. Thus, single-molecule techniques are particularly amenable for the study of Hsps and have begun to be used to reveal novel mechanistic details of their function. In this review, we discuss the current understanding of the chaperone action of Hsps and how gaps in the field can be addressed using single-molecule methods. Specifically, this review focuses on the ATP-independent small Hsps and the broader Hsp network and describes how these dynamic systems are amenable to single-molecule techniques.